A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a user drives a car by the guidance produced by navigation system. Such a navigation system detects the position of the user or user's vehicle, reads out map data pertaining to an area at the current vehicle position from a data storage medium. Alternatively, such map data can be provided to the user from a remote server through a communication network such as Internet and the like.
When a destination is set, the navigation system starts a route guidance function for guiding a user along a calculated guided route from the start point to the destination. During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments constituting the guided route in a memory. In the actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be clearly discernible from other routes. When the vehicle is within a predetermined distance from an intersection it is approaching, a highlighted intersection diagram with an arrow indicating the direction to turn at the intersection is displayed to inform the user of the appropriate road and direction at the intersection.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. When selecting a “Destination” menu on a main menu screen (not shown), the navigation system displays an “Find Destination By” screen as shown in FIG. 1B for specifying an input method for selecting the destination.
The “Find Destination By” screen of FIG. 1B lists various methods for selecting the destination. The methods include “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest” (POI) for selecting the programmed destination based on the name, category or telephone number. Other methods in the “Find Destination By” screen include “Recent Route” for specifying the destination based on the recent history of destinations saved in the system, “Address Book” for selecting the address of the destination out of the prescribed address list stored in the system, and “Today's Plan” for selecting two or more destinations.
When selecting, for example, the “Point of Interest” method, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1C. The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category of POI. If the “Place Type” is selected, the navigation system shows an “Select Category” screen such as shown in FIG. 1D.
Suppose the user selects “Restaurant”, the navigation system retrieves the POIs in the selected category, restaurant, in this case, as shown in FIG. 1E. Typically, names of POIs (restaurants) will be listed in the order of distance from the user (ex. current vehicle position). If the user selects a particular restaurant from the list, the navigation system displays a “Confirm Route” screen such as shown in FIG. 1F. In this example, the “Confirm Route” screen lists the name, address and phone number of the destination (POI specified by the user) . If this is the correct destination, the user enters an “Ok to Proceed” key to proceed to the next procedure.
In FIG. 1G, the navigation system calculates and determines a route to the destination, i.e., the selected POI. The navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. Then, the navigation system starts the route guidance as shown in FIG. 1H to guide the user along the calculated route to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions.
The foregoing is a typical example of using the “Point of Interest (POI)” input method of the navigation system. Because the recent storage medium provides a large volume of POI data, this input method can be used in various applications. For example, suppose a user is driving a car for a relatively long trip and the final destination is already specified, i.e., a calculated route to the destination is established. During the trip to the destination, the user wants to stop-by various places such as a gas station, restaurant, shopping mall, etc., along the calculated route. Alternatively, the user may simply want to enjoy seeing various places surrounding the calculated route to the destination by retrieving POIs along the route.
Such a situation is shown in FIG. 2A. As the vehicle indicated by VP moves to the destination (“Dest”), the user may want to stop by at a restaurant. Several restaurants exist along the guided route to the destination. Some restaurants are located close to the guided (calculated) route while others require a detour. Thus, it is helpful for the user if the navigation system provides information whether such POIs are easily accessible.
When searching POIs along the calculated route, the navigation system searches for POIs within a predetermined distance from the calculated route. FIG. 2B is a schematic diagram showing such a method of detecting POIs along the route to the destination. POIs 75a-75f of selected category are located along the route. A reference numeral 111 indicates the current position of the vehicle. A reference numeral 101 indicates the route to the destination calculated by the navigation system.
In this example, the navigation system creates a search range 113 which is formed, for example, by moving a search circle 135 on the calculated route 101. The navigation system will repeatedly check if POIs exist within the search range 113 by moving the search circle 135 on the calculated route and retrieves POIs within the search range 113. The outer edges of the search range 113 are denoted by lines 65a and 65b each of which has a distance Dt, for example, 0.3 miles, from the calculated route 101.
If POIs fall within the predetermined search range 113, the navigation system regards those POIs as accessible POIs and displays the information on the POIs. On the other hand, for POIs which do not fall within the predetermined range 113, the navigation system regards those POIs as non-accessible POIs and will not display the POIs. In this example, POIs 75a, 75c, 75e, and 75f are located within the search range 113, and thus retrieved by the navigation system. POIs 75b, 75d, 75g, and 75h are outside of the search range 113, and thus, not retrieved by the navigation system because they are not easily accessible.
FIG. 3 shows an example of method for searching POIs along the route as applied to an actual situation. The navigation system checks if the POIs exist within the search range 113 along the calculated route 101. As noted above, the search range 113 is created by incrementally shifting the search circle 135 on the calculated route 101. Among several POIs 123a-123e, the navigation system will retrieve only POI 123b as it falls within the search range 113.
When using the function of searching POIs along the route, the user is primarily interested in knowing about accessibility to the POIs, rather than mere distance from the calculated route. For example, there arises a case in which the geographical conditions allow the user to easily access a particular POI, even though its location is outside of the predetermined search range. Typically, when a POI is located on a street intersecting with the calculated route 101, the user can easily maneuver to the POI. In FIG. 3, the user can easily reach the POI 123a by making a left turn at a cross street 105a although the POI 123a is outside of the search range 113. Likewise, the user can easily access the POI 123d by making a right turn at the cross street 105b. 
Thus, there is a need of a new function of a navigation system for searching POIs along the calculated route based on accessibility to the POIs.